Above was obtained from /var/log/syslog after switching on hal debugging.

...and here is the /etc/fstab entry causing the problem

Now that /dev/sdb1 line was added manually by me post install. One aspect of GNU / Linux which can be a benefit is that it is infinitely configurable and can be tailored to your needs entirely.

As with all file level configurations, you take responsibility yourself for manual changes.

Simply commenting out that /dev/sdb1 line in /etc/fstab, returns my system to expected behaviour (automount of usb key).

Responses to the cause - volman or install alternative automounter:

There is no volman group on my system, your 'you are not privileged to mount' message may have a different cause. However in my case, the solution is clear above and does not involve creating any group or adjusting group membership.

First things lots of folks do when they receive an error message such as shown at the top of this article, is hunt around for another way for the system to automount.

Your mileage may vary, however if hal is giving you the error message then you might at least consider:

DAEMON_OPTS="--verbose=yes --use-syslog"

and rebooting your machine, to give you more information about what hal is unhappy about.

Why are you even running hal - the thing is deprecated?

In using an light desktop (Xfce), I try where possible to fit with it's default setup and work with it.

Thunar -> thunar-volman -> hal

...is a dependency chain that exists in Debian Squeeze, and gives a workable solution to automounting.

There are other alternatives - different automounters, or relying on udev rather than hal.

Notes and Further Reading:

Recap on the cause in my case: No fault of the system, purely a manual configuration change which I made, that blocked normal functioning of thunar-volman+hal